The present invention relates to a load cell that transmits and measures linear forces along and moments about three orthogonal axes. More particularly, a compact load cell body suitable for application as a wheel force transducer is disclosed.
Wheel force transducer or load cells for measuring forces along or moments about three orthogonal axes are known. The wheel force transducer typically is mounted between and to a vehicle spindle and a portion of a vehicle rim. The transducer measures forces and moments reacted through a wheel assembly at the spindle as the vehicle is operated.
One form of a wheel force transducer that has enjoyed substantial success and critical acclaim has been the Swift(copyright) transducer sold by MTS Systems Corporation of Eden Prairie, Minn. and is described in detail in U.S. Pat. Nos. 5,969,268 and 6,038,933. Generally, this transducer includes a load cell body having a rigid central member, a rigid annular ring and a plurality of tubular members extending radially and joining the central member to the annular ring. A plurality of sensing circuits are mounted to the plurality of tubular members. The rigid central member is mounted to the vehicle spindle, while the annular ring is attached to the vehicle rim. An encoder measures the angular position of the load cell body allowing the forces transmitted through the radial tubular members to be resolved with respect to an orthogonal stationary coordinate system.
Although the Swift(copyright) transducer is well suited for measuring loads reacted through the vehicle spindle on a vehicle such as passenger cars, the load cell cannot generally be used on a large vehicle such as an over-the-road truck due to a large spindle diameter on the truck leaving little clearance between the spindle and the tire rim.
There is thus an on-going need to provide an improved compact load cell, which can be used on large vehicles and is yet easy to manufacture.
One embodiment of the present invention is a load cell body for transmitting forces and moments in a plurality of directions. The load cell body is an integral assembly having a first ring member and a second ring member. Each ring member has a central aperture centered on a reference axis. Three or more tubes extend from the first ring member to the second ring member parallel to the reference axis.
Another embodiment includes a wheel force load cell body for transmitting forces in a plurality of directions. The wheel force load cell body has an integral assembly with first and second ring members. Each ring member has a central aperture centered on a reference axis. In addition, at least three tubes extend from the first ring member to the second ring member parallel to the reference axis. The wheel force load cell body also includes a mounting hub with first and second annular rims. The mounting hub also has a cylindrical support extending between the first and second rims.
Yet another aspect of the present invention includes a method of making a load cell body. The method includes fabricating from a single block of material an integral assembly having a first annular ring, a second annular ring and a plurality of members spanning therebetween. Each includes a central aperture centered on a reference axis. The method further includes forming a bore within each member, wherein each bore is aligned with an aperture in at least one of the annular rings.